Traditionally, crude oils are first distilled and then processed further as separate fractions. Conventionally, distillation is initially carried out under atmospheric pressure to produce various distillate fractions including naphtha and middle distillates, as well as an atmospheric residuum or "long" residuum which is then subjected to further distillation under vacuum to produce additional quantities of distillate material togehter with a vacuum residuum or "short" residuum. This processing scheme which initially separates the components of the crude according to their boiling points has conventionally been regarded as satisfactory because it enables the processing steps which follow the fractionation to be formulated according to the requirements of the individual fractions which vary not only according to their distillation characteristics but also in their chemical compositions.
It has now been found, however, that conventional processing schemes of this kind are not entirely favorable in that desirable reactions between components of different boiling ranges in the original crude may be carried out at an early stage and the characteristics of the treated crude may be favorably affected.